And C89 doesn't have the valid pointer requirement On Aug 21, 2015 7:03 AM, "David Bennett" <davidb at pfxcorp.com> wrote:
> Addressing only standards compliance, the C99 (n1256) standard says as > follows. > > 7.21.1 /2 > Where an argument declared as size_t n specifies the length of the array > for > a > function, n can have the value zero on a call to that function. Unless > explicitly stated > otherwise in the description of a particular function in this subclause, > pointer arguments > on such a call shall still have valid values, as described in 7.1.4. On > such > a call, a > function that locates a character finds no occurrence, a function that > compares two > character sequences returns zero, and a function that copies characters > copies zero > characters. > > Later versions of the standard contain similar wording. > > A zero value for the third argument of memset() is standards compliant. Any > warning by any compiler is for the convenience of developers and may be > safely disabled or ignored while remaining standards compliant. > > In my opinion, disabling or simply ignoring the warning are both legitimate > choices. Modifying the code to suppress the warning is NOT. > > Regards > David M Bennett FACS > > Andl - A New Database Language - andl.org > > -----Original Message----- > From: sqlite-users-bounces at mailinglists.sqlite.org > [mailto:sqlite-users-bounces at mailinglists.sqlite.org] On Behalf Of Scott > Robison > Sent: Friday, 21 August 2015 3:05 AM > To: General Discussion of SQLite Database > <sqlite-users at mailinglists.sqlite.org> > Subject: Re: [sqlite] Compile warnings > > On Thu, Aug 20, 2015 at 10:46 AM, Scott Doctor <scott at scottdoctor.com> > wrote: > > > My opinion is to keep it portable. The warning is there for a reason. > > you are worried about performance yet are calling a function that does > > nothing, which will take more memory cycles than a simple check for zero. > > > > I didn't say don't make a change. I'm observing there are things to > consider. In particular the optimization strategies that the SQLite team > have pursued for several years now have been *tiny* little optimizations > that would never be justifiable on their own but that really add up, > particularly for small devices probably running on batteries. > > > > Trying to memset a zero length is a bug, not the warning. Add an if > > statement around it. If the variable is local, it will probably be > > optimized as a register variable and a zero check of a register is a > > single op-code. > > > > Trying to memset a zero length buffer is not a bug if the length of the > sequence of bytes that needs to be set is zero. C89 in particular does not > disallow this use. > > > > the problem with disabling warnings is that even if this instance is > > not an error, some other part of the code may end up with the same > > situation but is an error in the coding. I would prefer code that can > > be compiled with all warnings turned on that gives no warnings than > > have a potential problem because of a glitch in the code. > > > > I don't think anyone called for disabling the warning. I think it should > just be ignored in this case, just as I ignore warnings that are generated > by Visual C++ when I compile SQLite there. > > -- > Scott Robison > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > > > _______________________________________________ > sqlite-users mailing list > sqlite-users at mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users >
